Patent GB-497648-A (GB)
Title: Improvements in or relating to the coating of aluminium or aluminium alloy articles
IPC: C25D11/18
Filed: 1937-05-22
Abstract: A substantially permanent self-lubricating surface is formed on articles of aluminium and aluminium alloys by coating with finely divided graphite, the graphite being applied in a suitable vehicle and being bonded to the surface by means of a substantially inorganic binder comprising an adherent aluminium oxide coating, an alkali metal silicate, or both.  The graphite is preferably applied in an aqueous dispersion formed, for example, by diluting the dispersion known under the Registered Trade Mark "Aquadag." The dispersion may be applied to an oxide coating formed on the aluminium article, or it may be mixed with a sodium silicate solution and applied direct to the metal surface after the latter has been cleaned and, if desired, etched, the treated surface being then dried in each case.  In the preferred method a mixture of the graphite dispersion and a sodium silicate solution is applied to an oxide-coated article, and the article then dried. The silicate used preferably has a silica to sodium oxide ratio greater than 2 to 1 by weight, e.g. it may be sodium disilicate or one of the higher silicates.  The treatment of articles such as screws, weather strips, pistons, and threaded rotating, or reciprocating parts in general is referred to; in an example pistons made of an aluminium-silicon alloy are anodized in 15 per cent sulphuric acid at 75 DEG  C. with a current density of 11-12 amps. per square foot, washed and dried, painted with a mixture of sodium silicate solution and diluted "Aquadag," allowed to dry, and then heated to 110 DEG  C. for an hour.  The bonding of graphite to aluminium or aluminium alloy pistons by means of an oxide coating only described and claimed in Specification 492,345, [Group II], is excluded from the scope of the invention.ALSO:A substantially permanent self-lubricating surface is formed on articles of aluminium and aluminium alloys by coating with finely divided graphite, the graphite being applied in a suitable vehicle and being bonded to the surface by means of a substantially inorganic binder comprising an adherent aluminium oxide coating, an alkali metal silicate, or both. The graphite is preferably applied in an aqueous dispersion formed, for example, by diluting the dispersion known under the Registered Trade Mark "Aquadag." The dispersion may be applied to an oxide coating formed on the aluminium article, or it may be mixed with a sodium silicate solution and applied direct to the metal surface after the latter has been cleaned and, if desired, etched, the treated surface being then dried in each case.  In the preferred method a mixture of the graphite dispersion and a sodium silicate solution is applied to an oxide-coated article, and the article then dried. The silicate used preferably has a silica to sodium oxide ratio greater than 2 to 1 by weight; e.g. it may be sodium disilicate or one of the higher silicates.  The treatment of articles such as screws, weather strips, pistons, and threaded, rotating, or reciprocating parts in general is referred to; in an example pistons made of an aluminium-silicon alloy are anodized in 15 per cent sulphuric acid at 75 DEG  C. with an electromotive force of 23 volts and a current density of 11-12 amps. per square foot, washed and dried, painted with a mixture of sodium silicate solution and diluted "Aquadag," allowed to dry, and then heated to 110 DEG  C. for an hour.  The bonding of graphite to aluminium or aluminium alloy pistons by means of an oxide coating only, described and claimed in Specification 492,345, is excluded from the scope of the invention.